(1) FIELD OF THE INVENTION
The present invention relates to a position indicator device for a conveyed object.
(2) DESCRIPTION OF THE PRIOR ART
A position indicator device of the above-noted type is used as means for obtaining position information of target objects such as eggs or fruits which do not meet a predetermined size or cleanliness standard, the target objects being continuously conveyed in alignment together with normal objects in a conveying passage.
Then, the obtained position information on the target i.e. defective objects is utilized as e.g. control information for automatically eliminating the same from the conveying passage.
According to a prior device known from a Japanese patent laid open gazette No. 62 166072, the indicator device includes a beam emitter for emitting a light beam towards an upper region of a checking area. In operation, the checking area is video-monitored from the above, such that a position of the indicator i.e. of a particular object within the area is detected based on a beam-reception position on the video monitor image. Another prior device is known from a Japanese patent laid open gazette No. 62 129190. With this invention, there is provided a beam emitter for emitting/scanning a light beam on each of a plurality of objects, the emitting/scanning operation being effected two-dimensionally from the above of a checking area. On the other hand, the indicator device per se includes a beam receiver. A position of a particular object is obtained based on a scanning position of the light beam received by the receiver.
However, with the above two prior devices, since the means for detecting the position of the indicator is disposed at the upper region of the checking area, there occurs a possibility of the means interfering with the view of a checking attendant observing objects being conveyed within the area.
In view of the above inconvenience, a further reference of a Japanese patent laid-open gazette 62-125887 suggested an improvement, in which an indicator device includes a supersonic wave emitter and there is disposed a plurality of corresponding receivers at each corner of a checking area. With this construction, the position of the indicator is obtained based on a delay between the emission of the emitter and the reception of the receiver.
However, with this construction also, a position detection is effected by maintaining the indicator at a predetermined altitude from the conveying surface. Then, since it is difficult for an inexperienced operator to move the indicator precisely to the predetermined altitude, there tends to occur a detection error.
That is to say, with the video monitoring method, when an inexperienced operator perpendicularly moves the indicator home positioned at a predetermined altitude, there occurs a variation in the beam reception position on the monitor image, whereby there tends to occur such detection error of mistaking another object for the target object.
Similarly, with the method utilizing a supersonic wave, a detection error occurs as well since such perpendicular movement by an inexperienced operator of the horizontally home-positioned indicator results this time in a variation in the distance between the wave emitter and the wave receiver.
According to a still further reference, a Japanese patent laid open gazette No. 61-70476, in order to regulate or limit such perpendicular displacement of the indicator, there is attached to an end of the indicator an arm which is movable only in the horizontal direction.
However, with this reference also, there remains the problem of the arm occasionally blocking the view of the conveyed objects thereby interfering with the visual checking operation.